The present invention relates to signal transformers and more particularly to a single bobbin transformer having multiple delink windings for controlling magnetic coupling.
Signal transformers are magnetic devices which are used in electric circuits. Such transformers have two or more coils which are wound on a core made from a magnetic material, typically iron. When an electric current is connected to one such coil, a magnetic field is produced which interacts with the other coils on the transformer core. If the magnetic field is time-varying, a voltage will be induced across the other coil or coils. Similarly, a time-varying current in the second coil will give rise to a voltage across the first coil. This mutual interaction between two coils is described by the term mutual inductance. In a transformer with two coils, one is known as the primary winding and the other as the secondary winding.
Signal transformers are used in various applications, including as component parts in televisions, radios, and other communication devices. For example, such transformers are useful in circuits which drive the audio-output (e.g., loud-speaker) in television sets and radios. Other signal transformers, known as Intermediate Frequency ("IF") transformers, are used in the signal processing circuitry of radios and televisions. Radio Frequency ("RF") transformers are used in the tuning stages of radios and televisions.
In designing signal transformers, various electrical parameters must be considered, such as the inductance of each coil, the mutual inductance between the coils, the currents, voltages, and frequencies at which the transformer will be operating, and the efficiency of the transformer. The present invention relates to the aspect of transformer design dealing with the control of the "coupling factor", or mutual inductance between multiple windings in a miniature signal transformer.
In past signal transformer designs, control of mutual inductance has been achieved by varying the space between the windings on the transformer core. As a result, the physical size of a given transformer designed to have a small mutual inductance could end up quite large, with respect to a similar transformer having a larger mutual inductance.
The practice of controlling the amount of coupling by varying the space between transformer windings necessitates the use of different size cores or bobbins, for different transformers. A large inventory of such bobbins must therefore be maintained by a transformer manufacturer. The use of different size bobbins also requires adjustments to be made to the transformer winding machinery, to accomodate the different bobbins.
It would be advantageous to provide a signal transformer design wherein the inductive coupling between transformer coils can be controlled by a method other than variations in the spacing of the coils with respect to each other. Such a transformer should enable the size of the transformer to be minimized while allowing electronic factors such as Q (efficiency) and K (inductive coupling) to be optimized. Further, it would be advantageous to provide a method of winding such a transformer where the primary and secondary coils can be wound simultaneously, resulting in a decrease in the time required to manufacture the transformer.
The present invention relates to such a transformer and the method of making it.